Conventionally, in the field of information recording/reproduction devices that use an optical disc such as a CD (Compact Disc) or DVD (Digital Versatile Disc), various methods have been proposed for performing tracking correction and cross talk cancellation (hereafter, referred to as ‘CTC’), and currently, a method of converting the light emitted from a light source into three beams, a main beam (0-dimension light) and two sub beams (±1-dimension light), and using the main beam and sub beams to perform tracking correction or CTC has become typical (for example, the differential push pull (DPP) method).
The tracking correction method or CTC method that uses these three beams has the characteristic that the positional relationship of where these three beams are shone onto the tracks that are formed on the disc surface is predetermined, and when this relationship of where the beams are shone is lost, it is no longer possible to perform tracking correction or CTC properly. For example, in the DPP method, it is necessary to maintain a relationship of opposite phase between the push-pull signal of the main beam and the push-pull signals of the sub beams, so it becomes essential that both sub beams be shone in the track normal direction onto positions that are spaced a half track pitch apart from each other (in other words, are shone onto the land tracks), and when this positional relationship is lost, it is no longer possible to obtain an accurate tracking error signal.
On the other hand, the track pitch of the optical disc differs depending on the current recording format, so in the case of a so-called compatible recorder (device that records data onto or reproduces data from optical discs having different recording formats), various designs have been proposed depending on the type of optical disc having differing recording formats in order to satisfy the positional relationship described above. For example, in Japanese patent application H5-144075, a method is proposed in which, in order to make tracking correction possible, the positions where the beams are shone are adjusted by rotating the diffraction grating according to the type of optical disc.